Density in recording information in a single recording surface has increased recently in accordance with an increase in capacity of a hard disc and such in a computer apparatus. Surface record density should be increased in order to increase recording capacity per an area of a magnetic disc, for example. A recording area per a bit in a recording medium, however, decreases according to an increase in record density. A decrease in size of a bit causes energy included in information of a bit to get closer to heat energy in a room temperature. Accordingly, there is a problem of heat demagnetization such as reversal and disappearance of recorded information due to thermal fluctuation and the like.
An in-plane recording system, which has been generally used, is a system of recording magnetism so that a direction of magnetization would be faced to an in-plane direction of a recording medium. In this system, however, easily occurs the above-mentioned disappearance of recorded information and such due to heat demagnetization. Accordingly, the system is changing to a perpendicular recording system in which a signal of magnetization is recorded in a direction perpendicular to a recording medium for the purpose of solving such a disadvantage. The perpendicular recording system is a system in which magnetic information is recorded in a recording medium according to the principle that a single magnetic pole is brought close. The recording magnetic field is faced to a direction substantially perpendicular to a recording film in accordance with the perpendicular recording system. Information recorded in a perpendicular magnetic field is easy to keep stability in energy since it is difficult for the pole N and the pole S to form a loop in a surface of the recording film. Accordingly, the perpendicular recording system has a more tolerance to heat demagnetization than the in-plane recording system.
Recent recording media, however, are required to have further higher density according to the need for recording and reproducing a greater quantity of information having higher density. In order to meet the requirement, introducing has been a recording medium having a great coercivity for the purpose of keeping influence of adjacent magnetic sections and thermal fluctuation to a minimum. This makes record of information in a recording medium difficult even in the case of the above-mentioned perpendicular recording system.
In order to solve such a disadvantage, proposed has been a hybrid magnetic recording system in which spot light formed by converging light or near field light is used to locally heat a magnetic section and temporarily reduce the coercivity while writing is carried out. Especially in the case of using the near field light, it is enabled to handle optical information in a region lower than a wavelength of light, the wavelength being a limit in a conventional optical system. Accordingly, the density of a recording bit can be made higher than that of a conventional optical information recording and reproducing device.
Various kinds of recording head having the above-mentioned hybrid magnetic recording system have been proposed. Among them, known has been a thin film magnetic head in which near field light is used for heating (JP-A-2007-164935 and JP-A-2007-164936).
The thin film magnetic head comprises a writing element chiefly having a main magnetic pole layer and an auxiliary magnetic pole layer and a near field light generation layer for generating near field light. The writing element and the near field light generation layer are covered with a coating layer and fitted on a side surface (an element forming surface) of a slider fixed to a top end of a load beam in order. Top ends of the main magnetic pole layer, the auxiliary magnetic pole layer and the near filed light generation layer are exposed from the coating layer and arranged to face the recording medium.
The main magnetic pole layer is connected to the auxiliary magnetic pole layer inside the coating layer. This makes the main magnetic pole layer and the auxiliary magnetic pole layer form a single magnetic pole type perpendicular head in which one magnetic pole (a single magnetic pole) is vertically provided. A coil layer is provided between the main magnetic pole layer and the auxiliary magnetic pole layer so as to be insulated from the both layers. The main magnetic pole layer, the auxiliary magnetic pole layer and the coil layer form an electromagnet as a whole.
The near field light generation layer is a metal layer made of various kinds of metal materials and formed so as to be adjacent to the main magnetic pole layer. It is formed so as to be tapered toward the top end faced to the recording medium. A laser beam incident on the near field light generation layer is arranged to cause the near field light to be generated from the top end. The coating layer is a layer functioning as an optical waveguide for introducing a laser beam emitted from an optical fiber to the near field light generation layer. The coating layer has a multi-layer structure in which layers formed from different materials are laminated.
On the other hand, the slider having the writing element and the near field light generation layer, which are covered with the coating layer, is generally fixed to the top end of a load beam so that its position can be changed. Moreover, an optical fiber for introducing a laser beam to the slider is fixed to the load beam. The optical fiber is fixed so that its top end would not be in contact with the slider. Accordingly, the laser beam emitted from the top end of the optical fiber is incident on the coating layer after transmission in the air and advances in the coating layer to reach the near field light generation layer.
In the case of using a thin film magnetic head having such a structure, the near field light is generated while the recording magnetic field is simultaneously operated so that various kinds of information would be recorded in the recording medium.
That is to say, a laser beam is radiated from the optical fiber to the coating layer. The laser beam advances in the coating layer and reaches the near field light generation layer. The laser beam then causes free electrons in the near field light generation layer to be oscillated evenly, so that a plasmon is excited, and thereby, the near field light is generated at a top end part locally. As a result, the near field light locally heats the magnetic recording layer of a recording medium and the coercivity is temporarily reduced.
Further, supplying a coil layer with a driving electric current at the same time as radiation of a laser beam allows the recording magnetic field to be locally applied to the magnetic recording layer of a recording medium, which is close to a top end of the main magnetic pole layer. As a result, various kinds of information can be recorded in a magnetic recording layer whose coercivity is temporarily reduced. That is to say, cooperation between the near field light and the magnetic field enables record in a recording medium to be achieved.